A citizens group said it measured high radiation levels at candidate venues for the 2020 Tokyo Olympics, but the metropolitan government disputes the data and the International Olympic Committee has shown little interest.

The group said some of the potential venues for the Summer Games had radiation levels exceeding the Tokyo metropolitan government’s standards for decontamination: 0.23 microsievert per hour 1 meter above ground or a hot spot that measures at least 1 microsievert per hour higher than the surrounding areas.

The site with the highest airborne radiation level was Yumenoshima Stadium in Tokyo’s Koto Ward. Located within Yumenoshima Park, the site has a nearby canal where yachts are anchored.

For the 2020 Games, the stadium and the 12 adjacent baseball fields will be plowed over. Facilities are planned there for equestrian events, such as dressage and jumping.

Group members said a reading of 0.484 microsievert per hour was detected 5 centimeters above ground in shrubs next to an entrance on the southern side of the stadium. They said they did not know why such a high reading was found.

Soil from the site had 3,040 becquerels of radioactive cesium per kilogram.

Other sites with comparatively high radiation levels 5 cm above ground were the Tokyo Metropolitan Gymnasium in Shibuya Ward, the projected venue for table tennis, and Yoyogi Gymnasium in the same ward, where the handball competition will be held.

The Uminomori cross country course near Tokyo Bay that is being considered for the equestrian eventing competition had a reading of 0.29 microsievert per hour at a height of 1 meter, the group said.

“The central and Tokyo metropolitan governments have not informed athletes and audiences around the world about data concerning possible radiation exposure,” said Takehiko Tsukushi, 70, who formed the citizens group. “If that is the case, I felt it was our moral responsibility as citizens to conduct the measurement and inform people, regardless of whether they support or oppose having the Olympics in Tokyo.”

The group measured radiation levels at candidate venues in Tokyo, Kanagawa and Saitama prefectures, but it could not cover all 37 sites that could host Olympic events.

The group did not take measurements at the candidate venues in Hokkaido and Miyagi Prefecture because of their distance from Tokyo. And it could not measure radiation levels at the Uminomori mountain bike course because it is still under construction.

After the 2011 meltdowns at the Fukushima No. 1 nuclear plant, Tsukushi, who lives in Tokyo’s Kita Ward, became a member of a group that sought to protect the ward’s children from radiation.

In late March this year, he began seeking members for a new group to measure radiation levels at Olympic venues. Over 14 days in April and May, 92 people of various ages and occupations took radiation measurements using their personal dosimeters.

The group selected a maximum of nine spots above asphalt and grass at each site. Three measurements were taken at each spot at heights of 5 centimeters and 1 meter. The median measurement was used to reduce error.

While hot spots have been detected mainly in eastern Tokyo, the group found readings close to 0.15 microsieverts per hour in a number of other locations, including Chofu in northwestern Tokyo and the Saitama Prefecture cities of Asaka and Kawagoe.

“We believe the data shows that radioactive materials have spread throughout the Kanto region, and that there are some hot spots within that wider area,” Tsukushi said.

The Tokyo metropolitan government’s standard for decontamination 1 meter above ground is based on the recommendation of the International Commission on Radiological Protection (ICRP), which set maximum annual radiation exposure levels for citizens at 1 millisievert (1,000 microsieverts), excluding background radiation and radiation from medical treatment.

Tsukushi’s group translated its findings into English and French and sent a report to then IOC President Jacques Rogge and about 200 national Olympic committees in June.

The group has not heard back from any of those organizations.

The head of the planning section under the environment improvement department at the Tokyo metropolitan government indicated the capital would not seek decontamination work based on the group’s data.

“It is difficult for us to make a judgment with the data collected, even if someone said there was a problem,” the official said.

The Tokyo metropolitan government measured airborne radiation levels at 100 locations in June 2011. It also conducted aircraft monitoring in September 2011.

However, it did not find any areas or hot spots that exceeded the standards set for decontamination work.

Any location with a possible annual radiation level exceeding 1 millisievert is designated by the central government for extensive study on radiation contamination.

No location in Tokyo has ever received such a designation.

The metropolitan government has continued measuring airborne radiation at eight monitoring posts throughout Tokyo, but the readings remain low.

Radiation measurements have been conducted at the Tokyo Metropolitan Institute of Public Health in Shinjuku Ward since before the 2011 nuclear accident.

The highest reading recorded there was about 0.15 microsievert per hour in late March 2011, soon after the Great East Japan Earthquake and tsunami. Subsequent readings have fallen. Between January and September this year, the maximum daily reading has hovered between 0.0373 and 0.0666 microsievert per hour.

The seven other monitoring posts have not shown any worrisome radiation levels.

Before the Fukushima nuclear accident, radiation readings at the Shinjuku institute were between 0.028 and 0.079 microsievert per hour, or levels similar to current measurements.

Although the Tokyo metropolitan government disagrees with the group’s findings of hot spots, Kunikazu Noguchi, an associate professor of radiation protection at Nihon University, has a different take.

“There is no doubt that some Olympic venues with higher than normal airborne radiation levels have been contaminated,” he said.

Noguchi said he believes that radioactive materials have spread throughout the greater Tokyo metropolitan area, and that concentration levels differ within the area.

Radiation levels can increase over dirt that absorbs cesium or in grass. Other areas where cesium tends to concentrate include roadside ditches or under gutters where rainwater containing cesium may flow.

Noguchi said such conditions may exist at some Olympic venue sites.

“In both the Tohoku and Kanto regions, we are now at a stage of moving from an emergency situation to a more normal one,” Noguchi said. “In order to move back to a normal situation as quickly as possible, the basic principle for radiation protection is to quickly decontaminate any area where readings exceeding 0.23 microsievert per hour are found, even if the finding is isolated.”

He added that decontamination would be a very simple matter of removing the soil because the area of high radiation is quite confined.

Other local governments have taken decontamination measures.

“If we receive reports about high radiation levels, even if it is isolated, we will conduct another measurement in that area,” an official with the Saitama prefectural government said. “And if decontamination standards are exceeded, the manager of the facility in question will decontaminate the area.”

The Kanagawa prefectural government said it takes similar action.

However, the Tokyo metropolitan government continues to insist there is no need for decontamination for isolated cases because those areas do not fall under the guidelines established by the decontamination standards.

During news conferences to promote Tokyo’s Olympic bid, Tokyo Governor Naoki Inose repeatedly said: “Radiation levels in Tokyo are no different from those in New York, London and Paris. There is no problem.”

Noguchi said the Tokyo metropolitan government should measure radiation levels at the venues and release the data to back up Inose’s argument.

“Saying there is no problem without even measuring for radiation is the same response as the Democratic Party of Japan government immediately after the Fukushima nuclear accident,” Noguchi said. “As host nation for the Olympics, it is imperative that radiation levels at the venues be released to the world.”